CSCE 120: Learning To Code

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1 CSCE 120: Learning To Code Organizing Code I Hacktivity 9.1 Introduction Prior to engaging in this hacktivity, you should have completed all of the pre-class activities as outlined in this module. At the start of class, you will be randomly assigned a partner to work with on the entirety of this hacktivity as a peer programming activity. Your instructor will inform you of your partner for this class. One of you will be the driver and the other will take on the navigator role. Recall that a driver is in charge of the keyboard and computer while the navigator is in charge of the handout and directing the activity. However, you are both responsible for contributing and discussing solutions. If you were a driver/navigator in the prior activity, switch roles for this activity. 1 Knowledge Check With your partner, discuss and answer each of the following questions. Write your answers down on a separate sheet of paper or type them up in a plain text file. 1. What is a function signature? What are the three parts of a function s signature? 2. Consider the following piece of code: 1 var x = 10; 2 var y = 20; 3 var z; 4 function compute(a, b) { 5 return (a + b) / 2; 1

2 7 z = compute(x, y); 8 x = compute(y, z); What are the values of the variables x, y, and z after this code executes? 3. Consider the following piece of code: 1 var x = 10; 2 var y; 3 function add(a) { 4 a = a + 5; 5 } 6 y = add(x); What are the values of the variables x, y after this code executes? 4. Consider the following piece of code: 1 function compute(a, b, c) { 2 if(c === undefined) { 3 c = 25; 4 } 5 return (a + b + c) / 3; What value is returned on the following function calls? a) compute(10, 20, 30);, b) compute(10, 20);, c) compute(10);, 5. What syntax would you use to make the add and compute functions part of an object named MyFunctions? 6. What is a callback? How and why would you use one? 7. What is an anonymous function and why would you use one? 2 Warm-up Exercises Download the code we ve provided from GitHub using the URL, com/cbourke/functionexercises. Open the project in Light Table and open the file, exercises.js. Complete the following exercises. 2

3 1. Write a function to convert from Celsius to Fahrenheit. Then write a function to convert from Fahrenheit to Celsius. Test your function with various values. The formulas for these conversions are as follows. c = 5 (f 32) 9 f = 9 5 c + 32 Test your functions with some common values of Celsius and Fahrenheit. 2. Rewrite the two temperature functions to be members of an object named TemperatureUtils 3. Recall that the natural logarithm, ln(x) is the logarithm with base e = You can use the natural logarithm to compute the logarithm using any base b > 0 using the formula log b (x) = ln(x) ln(b) Write the following function that takes two arguments where the second argument is the base, b. However, write your function so that b is optional: if it is not provided, it should use default natural logarithm. 1 function logarithm(x, b) { 2 } Recall that the math library provides a function to compute the natural logarithm: Math.log(). Test your functions with the following values: x = 64, b = 2 should be 6 x = 64, b = e should be x = 64, b = 10 should be An investment may pay you dividends, but over time inflation also tends to reduce your returns. To compute your inflation-adjusted returns, you can use the formula: ( ) 1 + investment return rate inflation rate Write a function that takes two parameters and computes the inflation-adjusted return rate. Both rates are on the scale [0, 1] while the output will be on the scale [0, 100]. Test your function with the following values: Investment Rate Inflation Rate Inflation-Adjusted

4 5. Write a function that takes two numbers: a, b and compares their values. Design the function to return: 1 if a < b 0 if they have the same value 1 if a > b This is known as a comparator function. Name your function cmpnumeric. 6. Write a similar comparator function that takes two student objects a, b and orders them by last name/first name. It should return: 1 if a s name comes before b s name 0 if they have the same names 1 if b s name comes before a s name Be sure to handle the situation where they share the same last name, but different first names. Test your function with several examples using the following formatting. Name your function cmpperson 1 var john = { 2 firstname: "John", 3 lastname: "Student" 4 }; 5 var jane = { 6 firstname: "Jane", 7 lastname: "Doe" 8 }; 7. Write a function that takes an array of numbers as an argument and returns the maximal element in it. 8. Now suppose that we wanted to write a function to find the maximum value in an array of strings. We d have to write another function. Now suppose we wanted to find the maximum value among an array of objects representing students: we would have to write dozens of functions for each criteria (the maximum with respect to name, GPA, class rank, etc.). A better solution would be to write a general purpose getmax() that could work with array of any type of data (not just numbers). To do this, we ll provide the getmax() function with a comparator callback function that is responsible for ordering pairs of data by returning something negative, zero, or something positive depending on the relative ordering of two elements. Consider the following (incomplete) solution. 4

5 1 function getmax(arr, cmp) { 2 var max = arr[0]; 3 for(var i=1; i<arr.length; i++) { 4 if(cmp(max, arr[i]) ) { 5 max = arr[i] 7 } 8 return max; 9 } Discuss what each line in this function does. Then determine what code is missing and implement this function. Fully test your function with the provided data and the comparator functions that you previously implemented. 5